Coating layer forming machine and method of forming it

ABSTRACT

A coating layer forming apparatus for minimizing the amount of the coating solution when forming a coating layer on a part and enhancing a dimensional precision of a formed surface of the coating layer. The coating layer forming apparatus has a rotation supporting device, a feeder ( 15 ), a layer former, and a coating removing device, maintains the inclined angle of a coating former for forming the coating layer at 30 to 70 degrees with respect to a tangential direction of rotation of a coating of a coating surface, and removes excess coating solution deposited on the coating former by a coating removing device.

TECHNICAL FIELD

The present invention relates to a coating layer forming apparatus forforming a coating layer on a surface to be coated of a part and a methodto form the coating layer.

More particularly, it relates to a coating layer forming apparatus forobtaining a coating layer improved in dimensional accuracy of a slidingsurface and a lubricating effect of a sliding surface of a piston etc.and a method to form a coating layer.

BACKGROUND ART

Japanese Unexamined Patent Publication (Kokai) No. 8-173893 discloses acoating layer forming apparatus and a method to form a coated layer. Anexplanation will be given of the coating device disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 8-173893 with reference toFIG. 1.

A coating device 100 shown in FIG. 1 is provided with a coatingcontainer 101 above a base material 104. The coating container 101 isfilled with a coating solution 102. Below the coating container 101 atthe two ends of the base material 104 is arranged a shaft bearingsupport plate 103 for rotatably supporting the base material 104. Theshaft bearing support plate 103 was mounted on it a not shown drivemotor. The drive motor makes the base material 104 rotate in theillustrated clockwise arrow direction R.

Since the coating solution 102 flows out from a nozzle of the coatingcontainer 101, the coating surface 105 of the base material 104 made torotate by the not illustrated drive motor is coated on its entiresurface as if being wrapped by it along with the rotation. To level thethickness of coating solution 102 coated on the surface to be coated105, a blade 106 set to an inclined angle θ of 135° with respect to atangential direction of rotation of the base material 104 is provided atthe surface to be coated 105.

A front end 106a of the blade 106 is held at a clearance of 100 μm fromthe coating surface 105. Further, the front end 106a of the blade 106 isformed into a stepped portion so as to become thinner. The blade 106 isfixed to a block 107. The excess amount of the coating solution 102coated on the base material 104 is collected by the blade 106 and madeto flow downward via an inclined surface of the blade 106 while the notshown drive motor makes the base material 104 rotate five to six timesat 200 rpm. A solution receiving mechanism 108 for accommodating excessamount of the coating solution flowing down from a rear end of the blade106 is provided.

The coating device 100 is simply structured and operates by a singleprinciple, but suffers from the following disadvantages.

Since the coating solution 102 accommodated in the coating container 101is made to drop from the nozzle of the coating container 101 on to thecoating surface 105 of the rotating base material 104 by the free-falldropping method, the amount dropped changes in accordance with theamount and viscosity of the coating solution 102 accommodated.Therefore, to prevent insufficient coating, a large amount of thecoating solution 102 is made to drip on to the coating surface 105 ofthe substrate 104 and the excess amount of the coating solution isremoved by the blade 106 and stored in the solution receiving mechanism108, but the amount of the coating solution 102 consumed becomeslarge—which is uneconomical.

If a large amount of coating solution 102 is deposited on the coatingsurface 105 of the substrate 104, it cannot be fully removed by theblade 106, a coating of a uniform thickness cannot be formed, and itbecomes difficult to improve the quality of the coating by reducing thespeed of the substrate 104. If the speed of the substrate 104 isincreased, the time for forming the coating becomes longer and theproductivity is lowered.

The blade 106 is attached inclined so as to guide the excess coatingsolution 102 to the solution receiving mechanism 108 along its surface,the blade 106 is inclined to a blunt angle θ=135° with the rotatingcoating surface 105 of the substrate 104. That is, the blade 106 onlyscrapes off the excess coating solution 10 of the surface of the coatingsurface 105 of the substrate 104. The coating solution 102, however, hasviscosity, so the amount of coating solution removed by the blade 106changes in accordance with its viscosity. The thickness of the remainingcoating solution on the coating surface 105 also changes in accordancewith the viscosity. In this way, the quality of the coating film has alarge dependence on the viscosity.

As apparatuses other than the above coating layer forming apparatus, forexample, Japanese Unexamined Patent Publication (Kokai) No. 10-26081 andJapanese Unexamined Patent Publication (Kokai) No. 5-147189 disclose ascreen printing method to coat material on a piston or other members. Ina screen printing apparatus, however, the thickness of coated layer ofthe coating material becomes thin. To form a coating layer obtaining asufficient sliding function, repeated coating is necessary. Therefore,there are problems that multiple coating is required, the number ofsteps in the process is increased, an increase in the coating facilitiesbecomes necessary, and that the process of production becomes expensive.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a coating layer formingapparatus able to minimize the amount of the coating solution coated andto improve the accuracy of thickness of the coating layer formed by thecoating solution and a method of formation thereof.

Another object of the present invention is to provide a coating layerforming apparatus able to improve the quality and the dimensionalaccuracy of the coated layer by a coating blade even if the coatingaccuracy for coating the coating solution on the coating surface of apart is insufficient and a method of formation thereof.

Still another object of the present invention is to provide a coatinglayer forming apparatus able to improve the accuracy of thickness andquality of the coated layer regardless of the viscosity of the coatingsolution and a method of formation thereof.

Still another object of the present invention is to provide a coatinglayer forming apparatus able to improve the production efficiency of theformation of the coating layer and minimize the amount of the coatingsolution used and a method of formation thereof. Further, an object ofthe present invention is to provide a coating layer forming apparatusable to simplify the configuration of the coating layer formingapparatus and a method of formation thereof.

The coating layer forming apparatus according to the first aspect of thepresent invention comprises; a support portion for supporting inattachable, detachable and alignmentable manner; two ends of a part onwhich a coating layer is to be formed; a rotatingly support devicehaving a rotation drive portion for making said part supported by thesupport portion rotate, a feeder for feeding a coating solution to asurface to be coated of the part supported by the support portion; alayer forming device having a coating former inclined at an angle (θ) of30° to 70° with respect to a tangential direction of rotation of saidcoating solution fed from the feeder to the coating surface and having afront end held at a clearance of a coating solution thickness from thecoating surface; and a coating removing means for removing the amount ofthe coating solution deposited on the coating former of the layerforming device from the coating former.

The coating layer forming apparatus of the present invention explainedabove coats the coating solution coated on the coating surface by thelayer forming device, while making the outer diameter of the coatinglayer uniform. At this time, even if the coating solution is coatednonuniformly on the coating surface, since the coating solutionaccumulated as the excess coating solution at the triangularly shapedspace between the coating former and the coating surface of the partflows to the coating surface where it is insufficient, the coating layeris uniformly coated. Further, since the coating solution can be pressedto the coating surface by the coating former, the dimensional accuracyfor the outer diameter of the coating layer is improved. Further, evenif the coating solution of the coating surface coated from the feeder isnot uniform, since the coating former levels the excess coating solutionto make it uniform, it is possible to coat the coating solution in aring shape via a feed nozzle and possible to form a high precisioncoating layer even if coating via an immersion tank filled with thecoating solution is performed.

In the coating layer forming apparatus of the present invention, thecoating removing means removes excess coating solution deposited on thecoating former after the coating former of the layer forming apparatusforms the coating solution to the thickness of the coating layer.

As shown in this configuration, when the coating solution is depositedon the coating former, since the coating solution deposited on thecoating former is removed by the coating removing means, the dimensionalaccuracy of the coating layer is improved and it is possible to preventformation of projections on the surface of the coating layer. Further,it is possible to secure excess coating solution at the coating formerduring formation and press the coating solution, the dimensionalaccuracy and quality of the coating layer can be improved.

Further, in the coating layer forming apparatus of the presentinvention, the coating removing means is comprised of an outlet at thelayer forming side of the coating former provided at the layer formingdevice.

In shown in this configuration, by directly forming the coating removingmeans at the coating former, the excess coating solution is flowedthrough the outlet, and thus it is possible to secure a substantiallyconstant amount of the excess coating solution and coat it on thecoating surface. Also, the excess coating solution is reduced in stages.Therefore, it is possible to finish the surface of the coating layerwith a high accuracy.

Further, in the coated layer forming apparatus of the present invention,the layer forming device has a first coating former and an approximatelyparallel second coating former and has an outlet at the second coatingformer.

As shown in this configuration, by providing the second coating formerprovided with the outlet in addition to the first coating former, it ispossible to form the coating solution in two stages to improve theaccuracy of the coating layer. Further, when the excess coating solutionbecomes more than a certain amount in the first coating former, thefirst coating former is pulled back and solution is removed by thecoating removing means. During this time, the second coating formerforms the coating solution into a coating layer. By alternately removingthe excess coating solution deposited onto the first and second coatingformers in this way, it is possible to finish the surface of the coatinglayer with a high accuracy.

Further, the coating layer forming apparatus according to the secondaspect of the present invention comprises; a support portion forsupporting in attachable, detachable and alignmentable manner, two endsof a part on which a coating layer is to be formed; a rotatingly supportdevice having a rotation drive portion for making said part supported bythe supports rotate; a feeder portion for feeding a coating solution toa coating surface of the part supported by the rotating support device;a rotating layer forming device provided along a circumferentialdirection of a rotation body with a plurality of blade-shaped coatingformers each inclined in an angular range of 30° to 70° with respect toa tangential direction of rotation of said coating solution fed from thefeeder to the coating surface and formed at a clearance of the coatinglayer thickness from the coating surface; and a washing tank where thecoating formers are washed below the rotating layer forming device, therotation direction of the rotating layer forming device being oppositeto that of the rotation of the part.

Since the coating layer forming apparatus provides the rotation bodywith the first, second, third, and further coating formers inclined andthe coating former is configured so as to be washed in a washing tank,it is possible to finish the coating layer while either washing thecoating solution deposited on the coating former or washing it at theend of each forming process. Therefore, it is possible to form a highprecision coating layer.

Further, in the coating layer forming apparatus of the presentinvention, the rotating layer forming device successively intermittentlyrotates for each first forming step where the plurality of coatingformers form said coating solution into the coating layer.

As seen in this configuration, when the coating former forms the coatinglayer and excess coating solution is deposited on the coating former,the layer forming device rotates and finishes the coating layer by thenext coating former.

Further, in the coating layer forming apparatus according to the presentinvention, the rotation drive portion of the rotating support devicemakes the part rotate in a range of 5 to 200 rotations per minute in oneforming step and makes the rotational speed larger before making thecoating formers move away from the coating layer.

As in this configuration, when coating the coating solution on thecoating surface, the part is rotated at a low rotational speed, whilewhen forming and finishing the coating layer, it is rotated at a higherspeed than the first low rotation and the coating former is pulled awayfrom the coating layer surface so that projections are not formed on thesurface of the coating layer.

The method of forming a coating layer of the present invention comprisescentering and supporting two ends of a part and making a coating surfacerotate by a rotating support device, coating a coating solution from afeeder on the coating surface, forming a coating layer by a coatingformer inclined at an inclined angle of 30° to 70° with respect to atangential direction of rotation of the coating solution coated on thecoating surface and held at a clearance of the coating layer thicknessfrom the coating surface, removing the excess coating solution depositedon the coating former via a coating removing means, and forming acoating layer of a next forming step.

The method of forming a coating layer of the present invention arrangesthe coating former inclined in the range of 30° to 70° with respect tothe rotating tangential direction of the coating solution to form thecoating layer while interposing excess coating solution at the coatingformer and, when the excess coating solution is deposited more thannecessary or when shifting to the next forming process, removes thecoating former via the coating removing means and finishes the outersurface of the coating layer.

A cylindrical part rotates at a first speed, lower than a second speedused when positioning the coating former, to coat a coating solution ona surface of the cylindrical part.

In the method of forming a coating layer of the present invention, thecoating solution has a viscosity of 100 CP to 20,000 CP at a coatingtemperature of 25° C. and a shear rate of 100 S⁻¹.

By doing this, it becomes possible to form a coating layer with a goodsurface precision by a coating solution having a broad range ofviscosity.

The coating solution has an organic resin as a binder dissolved ordispersed in water or an organic solvent and a PTFE powder as a solidlubricant, including 10 to 100 parts by weight of PTFE powder based on100 parts by weight of the binder.

By doing this, the PTFE powder provides an excellent lubricating effectand it becomes possible to form a coated layer with a good surfaceprecision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a conventional coating layer formingapparatus.

FIG. 2 is a sectional view along with the line H—H in FIG. 3 of acoating layer forming apparatus according to a first embodiment of thepresent invention.

FIG. 3 is a plan view of the coating layer forming apparatus illustratedin FIG. 2.

FIG. 4 is a side elevation of a coating former and a coating surface ofa part according to the first embodiment of the present invention.

FIG. 5 is an enlarged front view of a rotating support deviceillustrated in FIG. 2.

FIG. 6 is a front view of the part according to the first embodiment ofthe present invention.

FIG. 7 is a front view of formation of the coating layer on the partillustrated in FIG. 6.

FIG. 8 to FIG. 10 are front views of nozzles of embodiments of thepresent invention.

FIG. 11A and FIG. 11B are views of a coating former of an embodiment ofthe present invention, wherein FIG. 11A is a plan view and FIG. 11B is aside elevation of FIG. 11A.

FIG. 12A and FIG. 12B are views of the coating former of anotherembodiment according to the present invention, wherein FIG. 12A is aplan view and FIG. 12B is a side elevation of FIG. 12A.

FIG. 13 is a sectional view of the coating layer formed on the part inthe state shown in FIG. 13.

FIG. 14 is a view of the relation of a controller, a coating tank, and afeeder in FIG. 2.

FIG. 15A to FIG. 15C are views of a coating layer forming apparatusaccording to a second embodiment of the present invention and a methodof formation thereof, wherein FIG. 15A is a plan view of a coatingremoving means provided at the coating former of the second embodiment,FIG. 15B is a sectional view along the line H—H of FIG. 15A, and FIG.15C is a side elevation of FIG. 15A.

FIG. 16 is a sectional side elevation of a coating layer formingapparatus according to a third embodiment of the present invention.

FIG. 17 is a sectional side elevation of a coating layer formingapparatus according to a fourth embodiment of the present invention.

FIG. 18 is a sectional side elevation of a coating layer formingapparatus according to a fifth embodiment of the present embodiment.

FIG. 19 is a sectional side elevation of a coating layer formingapparatus according to a sixth embodiment of the present invention.

FIG. 20 is a side elevation of a spray coating painter of the presentinvention.

BEST MODE FOR WORKING THE INVENTION

Embodiments of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to the attached drawings.

First Embodiment

A first embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained withreference FIG. 2 to FIG. 14.

FIG. 2 and FIG. 3 show a coating layer forming apparatus of the firstembodiment of the present invention. FIG. 2 is a side elevation of acoating layer forming apparatus along the line H—H in FIG. 3, while FIG.3 is a plan view of FIG. 2. FIG. 4 is a view of the relationship ofarrangement of the coating former 21 with respect to the coating surfaceD of a cylindrical part A as seen along the line H—H of FIG. 3. FIG. 5is a front view of a rotating support device of FIG. 2. FIG. 6 is afront view of the cylindrical part of FIG. 5. FIG. 7 is a front view ofthe formation of the coated layer on the coating surface of thecylindrical part to be coated of FIG. 6.

The coating layer forming apparatus 1 illustrated in FIG. 2 and FIG. 3is comprised, as main parts, of a rotating support device 2 for rotatingthe cylindrical part A, a feeder 15 for coating the coating solution Bon the cylindrical part A, the layer forming device 20 for forming thecoated layer C from the coating solution B, a coating solution removingmeans 30 for removing the coating solution B deposited on the coatingformer 21 as excess coating solution E when forming it on the coatingsurface D by the layer forming device 20, and a controller 40 forcontrolling these parts.

The rotating support device 2 is configured as shown in FIG. 5.

In FIG. 3 and FIG. 5, the cylindrical part A is formed as shown in FIG.6. The cylindrical part A is a test piece a lubricating coating layer C′on a sliding surface of a piston. The coating layer C′ is formed on thesurface D of the test piece to be coated as shown in FIG. 6. The coatinglayer C′ is formed as explained above, then is processed by subsequentprocesses of the present invention, that is, a drying process and abaking process. The material etc. of the coating layer C will bedescribed later.

The cylindrical part A is provided at its two ends with conicalcentering holes. A positioner 5 of the rotating support device 2 isfitted into each centering hole F to position the mounting device of thecylindrical part A. Positioners 5 are provided at the two end surfaces6, 6 A facing the supports 4, 4 A. Also, an end surface 6 of one support4 is provided with a rotation member 4b for pressing against androtating the part A. Further, the other support 4 is provided with arotation drive 7, for instance, a motor, to make the positioner 4 androtation member 4b rotate.

Also, the other support 4A is configured to be movable so as to be ableto move horizontally by a movement means 9, that is, an air cylinder,via a guide rail 8 mounted on a support table 3. By using an aircylinder 9 to make the support 4A move in the X1 direction and open,setting the part A between the positioners 5, 5, and returning thesupport 4A in the X2 direction to close, the part A is easily mounted inthe rotating support 2. After the coating layer C is formed on thesurface D to be coated of the part A, the air cylinder 9 is used to openthe supports 4, 4 A and take out the part A.

In FIG. 2 and FIG. 4, the coating former 21 is arranged at a positionorthogonal to the axis of the cylindrical part A mounted in the supports4, 4 A. The coating former 21 is slidably mounted via a guide 22 and canrelatively move with respect to the cylindrical part A by a first drive23 (for example, an air cylinder or a motor turning a screw thread). Theguide 22 and the first drive 23 are fixed to a frame 24. The frame 24 ismounted at the support 4 via a shaft 13 so as to be rotatable. A seconddrive 25 comprised of an air cylinder or screw thread is designed to bemoved or rotated to enable adjustment of the inclined angle θ of thecoating former 21 with respect to the coating surface D of thecylindrical part A illustrated in FIG. 4. By this adjustment, thedistance between the tip of the coating former 21 and the coatingsurface D can be adjusted.

The inclined angle θ is so designed that the direction of the coatingformer 21 with respect to the tangential direction of rotation P of thecylindrical part A can be accurately adjusted to an acute angle, forexample, a range of 20°° to 80°. The inclined angle θ is preferably madewithin the range of 30° to 70°. The inclined angle θ is setcorresponding to the viscosity etc. of the coating solution B withinthis range.

Further, the frame 24 is configured so as to be able to be finelyadjusted in the vertical direction along an elongated hole 10 providedat the support 4.

The coating solution B to be shaped by the coating former 21 is coatedfrom a nozzle 16 of the feeder 15 arranged above the coating surface Don the coating surface D. Also, a solenoid valve 17 is provided at thefeeder 15. The coating solution B is filled and stored in a coating tank50 as shown in FIG. 2, FIG. 3, and FIG. 14. The coating solution B inthe coating tank 50 is delivered under pressure by compressed airintroduced from an air tank 51 via a pipe 52 coupled with an air tank51. The compressed coating solution B is supplied to the feeder 15through a tube 53 connecting the coating tank 50 and the solenoid valve17.

The coating solution B supplied to the feeder 15 is coated from thenozzle 16 by controlling the solenoid A valve 17 by a controller 40. Atthis time, the feeder 15 covers the coating surface D in the axialdirection by the five nozzles 16 formed as shown in FIG. 9, so byrotating the coating surface D, the coating solution B is coated in fiverings on the coating surface D. Further, when the width of the coatingsurface D in the axial direction is longer than the width of the nozzle16 as a whole of the feeder 15, the feeder 15 is made to move in theaxial direction of the part A by a third drive (air cylinder etc.) 11 tocoat the coating surface D in a spiral manner. Also, the feeder 15 canbe made to move by a fourth drive 12 so as to be able to move away fromor approach the cylindrical part A.

FIG. 8 is a front view of the nozzle supplying the coating solution ofFIG. 2. FIG. 9 is a front view of a nozzle showing another embodiment ofFIG. 8. FIG. 10 is a front view of a nozzle showing still anotherembodiment of FIG. 8.

The shape of the nozzle 16 is one shown in FIG. 8 to FIG. 10 in thepresent embodiment. In FIG. 8, there is one nozzle 16, so since thethird drive 11 also makes the cylindrical part A rotate while moving thefeeder 15 in the axial direction of the coating surface D, the coatingsolution B is coated spirally on the surface of the cylindrical part A.Also, if the coating solution B is coated without rotating thecylindrical part A, the coating solution B being coated linearly.

The nozzle of FIG. 9 is as explained above.

The nozzle 16 shown in FIG. 10 is formed to have a rectangular sectionalshape and the outlet of the coating solution B is formed in arectangular sectional shape, so the solution is coated in a strip overthe entire coating surface D of the cylindrical part A. When the widthof the outlet of the nozzle 16 is smaller than the width of the coatingsurface D, the solution is coated in a strip over the entire surfacealong with movement in the axial direction of the coating surface D bythe third drive 11.

Preferable embodiments of the coating former 21 in the layer formingdevice 20 are shown in FIG. 11A and FIG. 11B and in FIG. 12A and FIG.12B.

FIG. 11A is a plan view of a coating former, while FIG. 11B is asectional side elevation along the line H—H of FIG. 11A. FIG. 12A is aplan view of a coating former of another embodiment of the coatingforming device illustrated in FIG. 11B, while FIG. 12B is a sectionalside elevation along the line V—V of FIG. 12A.

The coating former 21 illustrated in FIG. 11A and FIG. 11B is comprisedof a layer former 35, front end 35a formed at the front end of the layerformer 35 in the form of a wedge by an inclined surface 36, and mountingholes 38 through which screws for fastening this coating former 21 tothe layer former 35 via a mount 28 pass. By arranging the front end 35aclose to the coating layer D of the cylindrical part A, the thickness ofthe coating coated on the coated layer D is made uniform. The inclinedsurface 36 is located at the side where the cylindrical part A and thefront end 35a face each other.

The coating former 21 illustrated in FIG. 12A and FIG. 12B has a layerformer 35, a front end 35b cut away at the front end of the layer former35 by a arc-shaped cross-section 36 A, and mounted holes 38. Thearc-shaped cross-section 36 A is located at a back side where thecylindrical part A and the front end 35a face each other. The width W ofthe front end 35b and the arc-shaped cross-section 36a prevent wavinessin the coating layer formed on the coating surface D of the cylindricalpart A.

The coated coating solution B coated on the surface of the cylindricalpart A is formed into the coating layer C by the coating former 21 asshown in FIG. 13. The thickness t of the coating layer C may be madewithin the range of 0.01 mm to 0.50 mm. Further, it was found byexperiments that the preferable thickness of the coating layer C wasfrom 0.02 mm to 0.30 mm. If the thickness of the coating layer C is morethan 0.30 mm, a certain time for the drying process is required toprevent a foaming during drying or baking. Further, if the thickness tbecomes more than 0.50 mm, the coating solution B will drip or thefoaming will occur at the time of drying or baking and it becomesdifficult to form the coating layer C′ obtained after drying and bakingto a uniform thickness.

If the lower limit of the thickness t of the coating layer C is lessthan 0.01 mm, if the cylindrical part A is used for a piston, thecoating layer C′ which is obtained after a drying or baking process' hasshortage in a lubrication action.

The present invention has another object to obtain the coating layerhaving lubricating effect C′ after completion of baking as the coatingsurface D when using the cylindrical part A as a piston.

Note that the thickness of the coating layer can be adjusted by forexample vertically adjusting the frame 24 along an elongated holeprovided in the support 4 to adjust the distance between the surface ofthe cylindrical part A and the front end of the coating former 21 andadjusting the inclined angle θ of the coating former 21 according to theviscosity of the coating solution.

The coating former 21 for forming the coating layer C is configured tobe adjustable to an inclined angle θ of 20° to 80° at the point ofcontact of the coating former 21 with respect to the tangentialdirection of rotation P of the coating surface D. If the inclined angleθ of the coating former 21 is made an angle smaller than 20°, thecontact area with the coating solution B is increased and buildupincreases a portion of the coating layer C. Also, if the inclined angleθ is more than 80°, the amount of the coating solution B scraped off bythe coating former 21 is increased and it becomes necessary to supply anexcess amount of the coating solution B. Therefore, the inclined angle θof the coating former 21 preferable in terms of quality is 30° to 70°.If so, the dimensional accuracy of the coating layer C was improved.

It was also observed that good results were obtained if the cylindricalpart A was rotated 30 to 200 revolutions per minute by the rotatingsupport device 2. If the rotational speed is made less than 30 rpm, thebuildup increases by an extreme amount on the surface of the coatinglayer C. Further, if the rotational speed is more than 200 rpm, bubblesare mixed into the coating layer C and the centrifugal force causes thecoating solution B to spray off or become wavy and the surface of thecoating layer C becomes nonuniform.

In FIG. 2 and FIG. 3, the coating removing means 30 moving reciprocallyin a direction orthogonal to a direction of movement of the coatingformer 21 is provided. The coating removing means 30 is provided with afifth driving portion (air cylinder) 14 for making a coating removingtool 31 reciprocally move guided along a recess 34 formed in a guide 22.The coating removing tool 31 is rectangularly formed and is coupled atits rear with the fifth drive 14. The front end is formed so as to slideon the upper surface of the coating former 21 and remove the excessamount of coating solution E.

The coating solution B of this embodiment used for the coating layerforming apparatus 1 is a heat curing type slidable coating. It iscomprised of an organic base resin as a binder and PTFE powder as asolid lubricant dissolved or dispersed in water or an organic solventand contains 10 to 100 parts by weight of PTFE powder with respect to100 parts by weight of the binder. The coating solution B of this rangeis excellent as a lubrication coating layer.

The lubrication coating layer must have a wear resistant ability,sliding ability, and sealing ability. The above mentioned compositionhas three abilities. If the PTFE powder is contained in an amount lessthan 10 percent by weight, the sliding ability becomes insufficient.Further, if the PTFE powder is contained in an amount over 50 percent byweight, the strength of the coating layer C′ after drying and baking isreduced.

As the organic resin of the binder, a polyamide resin, polyimide resin,polyamidimide resin, epoxy resin, silicone resin, polyphenylene sulfideresin, phenol resin, polyester resin, urethane resin, and the like wasused. These may be used alone or in mixtures of two or more types. Asanother compounding agent, a rheology control powder is used to adjustthe viscosity characteristic of the coating solution. Note that as thesolid lubricant, in addition to PTFE powder, it is possible to usegraphite and molybdenum disulfide, while as an additive, it is possibleto use a pigment, antifoaming agent, surfactant or the like.

Also, the viscosity of the coating solution B is preferably in the rangeof 100 CP to 20,000 CP. More particularly, a range of 1000 CP to 10,000CP is better. If less than 1000 CP, the coating solution B easily dripsfrom the coating surface D and it is hard to make the coating layer Cthick. Further, if over 10,000 CP, the leveling ability becomes poor, soto solve this, the coating time becomes longer and therefore theproductivity is reduced.

Note that the viscosity characteristics are measured using a cone platetype rotary viscometer. The viscosity was measured at 25° C. and at ashear rate of 100S⁻¹ (share rate).

FIG. 14 is a view showing the relation of connection of the controller,the coating tank, and the feeder illustrated in FIG. 2. The controller40, air tank 51, solenoid valve (working valve) 17, feeder 15, coatingformer 21, nozzle 16, and coating tank 50 are connected as illustrated.Details of the constitution illustrated in FIG. 14 will be given later.

The method of forming the coating layer of an embodiment according tothe present invention using the above coated layer forming apparatuswill be explained next.

The cylindrical part A used for the piston as shown in FIG. 6 or FIG. 7is produced by machining.

The cylindrical part A is set in the rotating support device 2 as shownin FIG. 5. In this setting, the other support 4A freely moving by themoving means 9 Is opened to attach the cylindrical part A to therotating support device 2, and the other support 4A is closed (state ofFIG. 5). At this time, the cylindrical part A is attached by thepositioner 5 in a specific position. The state of attachment of thisattached cylindrical part A in the coated layer forming apparatus 1becomes as shown in FIG. 2. This is the attachment step.

Next, by instruction of the controller 40, as shown in FIG. 14, the airtank 51 and the solenoid valve (working valve) 17 act and the coatingsolution B is coated on the coating surface D of the cylindrical part Afrom the nozzle 16 of the feeder 15. Simultaneously, the rotation drive7 rotates the cylindrical part A under the instruction of the controller40. The cylindrical part A is made to rotate by transmission of thepower of the rotation drive 7 to the cylindrical part A via the pivotmember 4b. The rotations speed is within a range from 30 rpm to 200 rpm.The rotation changes between two speeds with a first speed of 50 rpm anda second speed of 100 rpm. The change in speed is done immediatelybefore the separation of the coating former 21 of the layer formingdevice 20 from the coated layer C. This is the coating step of coatingthe coating solution B on the coating surface D of the cylindrical partA.

At the state where the coating solution B is coated on the surface to becoated D of the cylindrical part A, the coated layer C has an unevensurface, so the first drive 23 acts under the instruction of thecontroller 40 and makes the coating former 21 extend to the cylindricalpart A. Then, the front end surface of the layer former 35 of thecoating former 21 reduces the clearance 29 of the cylindrical part Awith the coating surface D to a range of from 0.02 mm to 0.50 mm.

The coating solution B is formed on the coated layer C by the coatingformer 21 while the cylindrical part A is being rotated at 50 rpm inthis state. In this embodiment, the clearance 29 between the coatingformer 21 and the coating surface D is held at 0.1 mm when forming thecoated layer C. This step is the coated layer forming step. Note thatthe excess amount of the coating solution is removed from the coatedlayer C by the coating former 21.

Note that the coating former 21 is adjusted to inclined angle θ by thesecond drive 25. This inclined angle θ is adjusted within a range offrom 20° to 80°, but in the present embodiment, it was set at 45θ.Further, the shaft 13 is moved along the elongated hole 10 by a notillustrated adjustment screw so as to finely adjust the positionrelationship (position in the Y-direction) between the layer former 35of the coating former 21 and the coating surface D.

Next, the excess amount coating solution E is stored in the layer former35 of the coating former 21 during the coated layer shaping step, butthe larger the excess amount of coating solution E, the worse theprecision of the circumferential surface of the coated layer C,therefore the excess coating solution E deposited on the coating former21 is removed by the coating removing means 30 at the stage where thecoating former 21 is retracted so as to improve the forming finishingwork of the layer former 35 at the time of formation in the nextformation step. This step is the coating removal step.

After going through such steps, the formation step of the coated layer Cis completed. At the same time of the completion of this formation step,the cylindrical part A formed with the coated layer C is taken out ofthe rotating support device 2. This cylindrical part A formed with thecoated layer C passes through the drying step and the baking step,whereby the formation step is completed. These drying step and thebaking step can be carried out by various facilities. This is the finalstep.

Note that, as another embodiment, if the excess amount of the coatingsolution E deposited on the coating former 21 becomes larger than theset amount, it is also possible for a not illustrated sensor to make thefirst drive 23 operate to return the former to the guide 22 and have theamount of the solution removed by the coating removing means 30. Thecoating former 21 then again extends to form the coated layer C.

Second Embodiment

A second embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to FIG. 15.

FIG. 15 shows a coating removing means 30B provided at the coatingformer 21 of a second embodiment of the present invention.

FIG. 15A is a plan view of the coating former 21 provided with thecoating removing means 30B. FIG. 15B is a sectional view taken along theline V—V in FIG. 15A. FIG. 15C is a side elevation of the coating former21 in FIG. 15A.

The coating former illustrated in FIG. 15A to FIG. 15C may be used asthe second coating former 21 described later.

In FIG. 15A to FIG. 15C, the coating former 21 is formed in a bladeshape, and the mounting portion 28 of the rear end is provided withmounting holes 38 for attaching to a holder 37 of the layer formingdevice 20. A layer former 35 is formed on the inclined surface at thefront end opposite to the rear end. The rectangular outlet 26 is formedat the bottom surface in the recess formed in the inclined surface 27from the two ends to the center at the layer former 35 side. The twosides of the inclined surface 27 are formed in stepped surfaces. Thestepped surfaces may also be formed as steep inclined surfaces from thetwo sides. The coating removing means 30B may be an outlet 26 providedwith a large number of holes.

The coating removing means 30B provided at the coating former 21 asdescribed above is mounted to the holder 37 shown in FIG. 2. Further,when the coating solution B is formed into the coating layer C by thecoating former 21, the excess amount of the coating solution E flows tothe outlet 26 of the coating removing means 30B and is removed.

When providing the coating removing means 30B, the coating removingmeans 30 shown in FIG. 2 is unnecessary, but it is also possible to usethe two. The rest of the configuration is similar to that of FIG. 2.

Third Embodiment

A third embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to FIG. 16.

FIG. 16 is a sectional side elevation of the coating layer formingapparatus 1 of a third embodiment of the present invention.

In FIG. 16, the point of difference from FIG. 2 is that the layerforming apparatus 20 is formed with functions corresponding to therotating layer forming device 20A and that the excess amount of thecoating solution E deposited on the contained former 21 of the rotatinglayer forming device 20A is washed off by solvent filled in the washingtank 30A. The washing tank 30A is provided with a jet nozzle 32. Thesolvent may be ejected from the jet nozzle 32 to strike and wash thelayer former 35.

In the third embodiment, the layer forming device 20 explained above isthe rotating layer forming device 20A. The rotating layer forming device20A is structured with disk-shaped flanges 18 welded to the two ends ofa cylindrical body 39 and with six blades welded equally arrangedbetween the flanges 18. The six coating formers 21, that is, blades, mayin accordance with need to be two, four, six, or eight formers.

In the rotating layer forming device 20A, each coating former 21 rotatesonce at the completion of each process for forming the coating layer C,but it is also possible to perform rough forming and fine forming byrotation of two coating formers 21 in one process. Further, it is alsopossible to rotate a plurality of formers in one process in accordancewith need. These are then operated by instructions from a controller 40.

Further, the washing tank 30A corresponds to the coating removing means30 in FIG. 2. The washing tank 30A is not illustrated, but is configuredto be able to freely move to and from the rotating layer forming device20A and designed to be able to adjust the depth of the washing solution.Note that reference numeral 48 denotes a supply pipe of the washingsolution. The rest of the configuration is similar to that shown in FIG.2.

Fourth Embodiment

A fourth embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to FIG. 17.

FIG. 17 is a side elevation of the coating layer forming apparatus 1 ofa fourth embodiment of the present invention.

In the coating layer forming apparatus 1 in the fourth embodimentillustrated in FIG. 17, the point of difference from the thirdembodiment is that a plurality of outlets 26 explained in the secondembodiment (refer to FIG. 15) are provided at the blade shaped coatingformer 21. The washing effect in the washing tank 30A is improved by theoutlets 26. The rest of the configuration is similar to the thirdembodiment.

Fifth Embodiment

A fifth embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to FIG. 18.

FIG. 18 is a side elevation of the coating layer forming apparatus 1 ofthe fifth embodiment of the present invention.

In FIG. 18, the point of difference from the coating layer formingapparatus shown in FIG. 1 is that the feeder 15 is formed in animmersion tank 15A. The immersion tank 15A is filled with the coatingsolution B. The immersion tank 15A is arranged below the rotatingsupport device 2. The cylindrical part A is coated on its coatingsurface D by rotation. The immersion tank 15A and the cylindrical part Aare designed to be able to move to and from with each other relativelyin the Y-direction. Movement in the Y-direction is performed by a sixthdrive 33. A signal is transmitted to the controller 40 from a levelsensor 49 provided within the immersion bath 15A. The sixth drive 33 isoperated based on instructions issued from the controller 40 to thesixth drive 33. The rest of the configuration is similar to the coatinglayer forming apparatus 1 shown in FIG. 2. The amount of the coatingsolution is adjusted in accordance with the depth to which thecylindrical part A is immersed in the coating solution B.

Sixth Embodiment

A sixth embodiment of the coating layer forming apparatus and method offormation thereof of the present invention will be explained next withreference to FIG. 19.

FIG. 19 is a side elevation of the coating layer forming apparatus 1 ofthe sixth embodiment of the present invention.

In FIG. 19, the point of difference from the coating layer formingapparatus 1 in FIG. 2 is that the coating former of the layer formingdevice 20 is comprised of the first coating former 21 and the secondcoating former 21a. This configuration is a two-stage configuration asshown in FIG. 19.

The coating former is sometimes comprised of two first coating formers21 arranged in parallel in two stages and sometimes comprised of thefirst coating former 21 and the second coating former 21a of the shapeshown in FIG. 14 arranged in two stages.

When one process of formation of the coating layer C is performed in thestate shown in FIG. 19, the first drive 23 coupled with the secondcoating former 21a is operated to make it retract during the formationof the coating layer C by the first coating former 21 and the excessamount of the coating solution E deposited on the layer former 35 isremoved using the coating removing means 30. Next, the second coatingformer 21a is advanced to form the coating solution B into the coatinglayer C at a high precision. During that time, the first coating former21 is retracted and the excess amount of the coating solution E isremoved by the coating removing means 30. That is, the first coatingformer 21 and the second coating former 21a are alternately operated toform the coating layer C.

Specifically, providing the second coating former 21a as a second stageprevents generation of excess amount of the coating solution E andprevents projections from being caused due to buildup of the solution atthe surface of the coating layer C.

Seventh Embodiment

Next, a seventh embodiment of the coating layer forming apparatus andmethod of formation thereof of the present invention will be explained.

In the coating layer forming apparatus 1 of the seventh embodiment ofthe present invention, in FIG. 3, the rotation drive 7 operates at a lowspeed at an initial stage of the formation of the coating layer C underinstructions of the controller 40. Next, when the coating layer C isclose to being finished, the speed is made higher than the initial one,the coating former 21 is retracted, and the process of formation of thecoating layer C is completed. The high speed rotation prevents theprojections from forming on the surface of the coating layer C due tobuildup of the excess amount of the coating solution deposited on thecoating former 21 and gives a high dimensional accuracy.

The two stages of rotation of the cylindrical part A in the seventhembodiment are obtained by controlling the rotation drive 7 by thecontroller 40. The two-stage rotation coating layer forming apparatus 1can be employed in the first embodiment to the sixth embodiment. Therotational speeds may, as explained above, be ones in the range of from30 rpm to 200 rpm. For example, the first rotational speed is made at 30rpm and the second rotational speed is made at 100 rpm. Alternatively,the first rotational speed is made at 60 rpm and the second rotationalspeed is made at 150 rpm.

EXAMPLES

Next, examples will be explained.

The cylindrical part A of the examples is the one shown in FIG. 6. Also,the coating former 21 is the former shown in FIG. 11 and is used it asthe first coating former 21 and the former shown in FIG. 15 is used asthe second coating former 21a for two-stage formation in the state ofthe FIG. 19.

Example 1

The cylindrical part A shown in FIG. 6 was set in the coating layerforming apparatus 1 of the present invention. The coating solution B wassuccessively coated in rings in one second at a time at three equalpoints equally arranged along the axial direction of the coating surfaceD using the nozzle 16 shown in FIG. 8 while rotating the cylindricalpart A at a first rotational speed of 60 rpm.

Next, the inclined angle θ of the coating former 21 of the layer formingdevice 20 was made at 45° and the layer former 35 was held at aclearance 29 of 0.2 mm with respect to the coating surface D to form thecoating layer C. After the coating solution B was coated, the rotationalspeed of the cylindrical part A was changed to 100 rpm and the coatingformer 21 was pulled away from the coating layer C. Next, thecylindrical part A was detached from the rotary support device 2 anddried and baked in an electric furnace under drying and bakingconditions. It could be observed that a uniform coating layer C wasformed on the cylindrical part A after the end of the baking. Note thatthe coating solution component after drying and baking included 30 wt %of PTFE powder and had a viscosity of 3000 CP.

Example 2

The same procedure was performed in Example 2 as with Example 1 exceptthe points described below.

(1) The rotational speed of the cylindrical part A was made at 30 rpm.

(2) The nozzle 16 shown in FIG. 9 comprised of smaller nozzles arrangedat five equal points equally arranged in the axial direction of thecoating surface D of the cylindrical part A was used.

(3) The coating solution B was coated for 2 seconds from the nozzle 16so as to form five rings on the coating surface D.

Example 3

The same procedure was performed in Example 3 as with Example 1 exceptthe points described below.

(1) The rotational speed of the cylindrical part A was made at 30 rpm.

(2) A nozzle 16 having an opening the same as the length in the axialdirection of the coating surface D shown in FIG. 10 is used.

(3) The coating solution B was coated for 2 seconds from the nozzle 16to rings on the coating surface D.

Example 4

The same procedure was performed in Example 4 as with Example 1 exceptthe points described below.

(1) The rotational speed of the cylindrical part A was made at 30 rpm.

(2) The coating solution B was coated on the entire surface of thecoating surface D from the immersion tank 15A.

Example 5

The same procedure was performed in Example 5 as with Example 1 exceptthe points described below.

(1) The same nozzle as in Example 1 was used to coat the coatingsolution B linearly in the axial direction of the coating surface D ofthe cylindrical part A.

(2) Next, the cylindrical part A was rotated and the coating layer C wasformed by the coating former 21.

Example 6

The same procedure was performed in Example 6 as with Example 1 exceptthe points described below.

(1) The rotational speed of the cylindrical part A was made at 30 rpm.

(2) The nozzle 16 shown in FIG. 9 comprised of smaller nozzles arrangedat five equal points equally arranged in the axial direction of thecoating surface D of the cylindrical part A was used.

(3) The coating solution B was coated for 2 seconds in rings on thecoating surface D.

Comparative Example 1

As shown in FIG. 20, a cylindrical part A was set on a rotation table111 in a vertical direction. A spraygun 110 was used to coat the samecoating solution B as each example on the surface of the coating surfaceby spray coating. This was then dried and baked under the sameconditions as the examples.

Comparative Example 2

The same procedure was followed as in Example 3, except the rotationalspeed was made 10 rpm and the coating time of the coating solution Bfrom the nozzle 16 was made 6 seconds. The inclined angle of the coatingformer was made one by which the front end was inclined upward by 45°opposite from Example 3.

Comparative Example 3

The same procedure was performed as in Example 6. Unlike Example 6,however, the excess coating solution of the coating former was notremoved.

Results of a comparison of Examples 1 to 6 and Comparative Examples 1 to6 of the present invention are given in Table 1.

TABLE 1 Amount of coating Average film used (per part) thickness Ex. 10.83 g 0.052 mm Ex. 2 0.83 g 0.055 mm Ex. 3 0.95 g 0.053 mm Ex. 4 1.03 g0.050 mm Ex. 5 0.96 g 0.050 mm Comp. Ex. 1 5.08 g 0.053 mm Comp. Ex. 23.00 g 0.056 mm

As clear from Table 1, in the case of the comparative examples, theamount used in the coating of the solution B increased in one coatinglayer process. Particularly, since the coating for the lubrication usecoating layer is expensive, when there are a large number of cylindricalparts A, the cost of the cylindrical part A increases.

Further, comparing Example 6 with Comparative Example 3, where only theremoval of the excess coating solution E of the coating former 21differs, it is observed that when the coating former 21 moves away fromthe coating surface D, the buildup of the coating surface formed by theexcess amount of the coating solution E increases in quantity withprogress of the experiments.

TABLE 2 Buildup of coating film (mm) 1st 2nd 3rd 5th 10th Ex. 6 0.02 mm0.02 mm 0.02 mm 0.02 mm 0.02 mm Comp. 0.02 mm 0.03 mm 0.04 mm 0.06 mm0.06 mm Ex. 3

As explained above, the coating layer forming apparatus of the presentinvention enables formation of a coating layer to be formed with theminimum amount of the coating solution by setting the coating former atan inclined angle and by the function of the coating removing means,enabling the amount of the expensive coating solution used to be reducedthereby reducing the cost of the part.

According to the present invention, the effect is exhibited ofpreventing buildup and waviness at the surface of the coating layer andenabling to form a high precision sliding surface.

According to the present invention, the effect can be expected that evenif the method of coating of the feeder of the coating solution issimple, the coating layer can be formed well and the device of thefeeder can be made at lower cost.

In the coating layer forming apparatus of the present invention, thelayer forming device is configured as a rotating layer forming deviceand the coating removing is device configured to remove the excessamount of the coating solution by the washing tank, so the coating layercan be formed in a short time and the productivity can be improved.

According to the present invention, since the excess amount of thecoating solution deposited on the coating former can be continuouslyremoved, high precision surroundings can be formed.

The method of formation of the present invention can reduce the amountof the coating solution used and thereby reduce the cost of the part.

The method of formation of the present invention improves thedimensional accuracy of the outer circumferential surface of the coatinglayer and facilitates in terms of quality control and enables to improvethe precision of formation even in the case of such a hard handlingcoating solution as solution for a lubrication coating layer.

INDUSTRIAL APPLICABILITY

The coating layer forming apparatus and the method of formation of acoating layer of the present invention can be used for coatings forpistons and various other coatings.

The above embodiments were explained with reference to coating a pistonas preferable examples, but the present invention may also be applied torotatable cylinders, shafts, and other objects.

1. A method of forming a coating layer comprising the steps of: making acylindrical part rotate at a first speed to coat a coating solution onthe surface of said cylindrical part, making said cylindrical partrotate at a second speed higher than said first speed when positioning afront end of a coating former in a predetermined clearance defining thecoating formation thickness with the surface of the cylindrical part atan acute inclined angle between the surface plane of the coating formerand a rotational tangential direction at the side of the coming surfaceof said cylindrical part to make a uniform coating solution deposit onthe surface of the cylindrical part, and making the cylindrical partrotate at a third speed higher than said second speed when alienatingthe front end of the coating former from the surface of the cylindricalpart and stopping the rotation of said cylindrical part.
 2. The methodof forming a coating layer as set forth in claim 1, wherein saidcylindrical part is made to rotate in a range of 50 to 200 rpm.
 3. Themethod of forming a coating layer as set forth in claim 1, wherein saidinclined angle is in a range of 30 to 80 degrees.
 4. The method offorming a coating layer as set forth in claim 1, wherein said coatingformer comprises a layer former and a front end of said layer formerfacing a rotating surface of said cylindrical part, a surface of saidfront end with respect to the direction of rotation of said cylindricalpart is flat, the front end has a predetermined thickness, and the rearside of the flat surface of the front end is formed cut away in an arcshape.
 5. The method of forming a coating layer as set forth in claim 4,wherein said layer former separated by a predetermined distance fromsaid front end of said coating former comprises a part for removingexcess coating solution.
 6. The method of forming a coating layer as setforth in claim 5, wherein the portion for removing the excess coating isa hole penetrating through the layer former.
 7. The method of forming acoating layer as set forth in claim 1, wherein the coating solution hasa viscosity of 100 CP to 20,000 CP at a coating temperature of 25° C.and a shear rate of 100 S⁻¹.
 8. The method of forming a coating layer asset forth in claim 7, wherein the coating solution is formed by anorganic base resin of a binder dissolved or dispersed in water or anorganic solvent and a PTFE powder, and includes 10 to 100 parts byweight of PTFE powder with respect to 100 parts by weight of the organicbase resin of the binder.
 9. A coating layer forming apparatuscomprising: a rotating support device having supports for detachablyattaching centered between them and rotatably holding two ends of acylindrical part on which a coating layer is to be formed and a rotationdrive for making said cylindrical part supported by the supports rotate;a coating feeder for coating a coating solution to a surface of thecylindrical part rotating and supported by the rotating support device;a layer forming device having a coating former, said coating formerbeing inclined at an acute inclined angel between the surface plane ofthe coating former and a rotational tangential direction at the side ofthe coming surface of the cylindrical part, and having a front enddirected downward and positioned at a predetermined clearance with thesurface of the cylindrical part; and a coating removing means forremoving the coating solution deposited on the coating former of thelayer forming device.
 10. The coating layer forming apparatus as setforth in claim 9, wherein the inclined angle of the coating former is ina range of 30 to 80 degrees.
 11. The coating layer forming apparatus asset forth in claim 9, wherein said coating former comprises a layerformer and a front end of said layer former facing a rotating surface ofsaid cylindrical part, said front end being inclined with respect to asurface of said cylindrical part.
 12. The coating layer formingapparatus as set forth in claim 9, wherein said coating former comprisesa layer former and a front end of said layer former facing a rotatingsurface of said cylindrical part, a surface of said front end withrespect to a surface of said cylindrical part is flat, the front end hasa predetermined thickness, and the rear side of the flat surface of thefront end is formed cut away in an arc shape.
 13. The coating layerforming apparatus as set forth in claim 11, wherein said layer formerseparated by a predetermined distance from said front end of saidcoating former comprises a part for removing excess coating solutionconstituting said excess coating removing means.
 14. The coating layerforming apparatus as set forth in claim 13, wherein the portion forremoving the excess coating is a hole penetrating through the layerformer.
 15. The coating layer forming apparatus as set forth in claim14, wherein the portion for removing the excess coating comprises holeshaving inclined surfaces passing through said layer former formed at aplurality of positions of said coating former parallel to the rotatingsurface of the cylindrical part.
 16. The coating layer forming apparatusas set forth in claim 9, wherein said layer former has at least onesecond coating former positioned at the rear side of said coating formerin the direction of rotation, shaped substantially the same as saidcoating former, inclined at the same angle as the coating former withrespect to the tangential direction in the periphery of the cylindricalpart, and separated from the surface of the cylindrical part by exactlythe same distance as the coating former.
 17. The coating layer formingapparatus as set forth in claim 16, wherein said layer former separatedby a predetermined distance from said front end of said second coatingformer comprises a part for removing excess coating solutionconstituting said excess coating removing means.
 18. The coating layerforming apparatus as set forth in claim 17, wherein the portion forremoving the excess coating comprises a hole penetrating through thelayer former.
 19. The coating layer forming apparatus as set forth inclaim 17, wherein the portion for removing the excess coating comprisesholes having inclined surfaces passing through said layer former formedat a plurality of positions parallel to the rotating surface of thecylindrical part.
 20. The coating layer forming apparatus as set forthin claim 9, wherein said layer forming device has a means for adjustinga distance between a front end of said coating former and a surface ofsaid cylindrical part.
 21. The coating layer forming apparatus as setforth in claim 9, wherein said rotation drive of said rotary supportdevice makes said cylindrical part rotate in a range of 50 to 200 rpm.22. The coating layer forming apparatus as set forth in claim 21,wherein said rotation drive increases the rotation speed of saidcylindrical part from a lower speed in said range of rotation.
 23. Thecoating layer forming apparatus as set forth in claim 9, wherein saidlayer former: separates the front end of the coating former from thesurface of the cylindrical part when the coating solution from saidcoating feeder is coated on the surface of said cylindrical part, makesthe front end of said coating former extend to a distance defining acoating layer from the surface of said cylindrical part when a coatingis coated on the surface of the cylindrical part, and makes the frontend of said coating former separate from the surface of said cylindricalpart after the coating layer is formed.
 24. The coating layer formingapparatus as set forth in claim 23, wherein said rotation drive of saidrotary support device makes said cylindrical part rotate in a range of50 to 200 rpm and said rotation drive makes said cylindrical part rotateat a low speed equal to or near 50 rpm when a coating solution from saidcoating feeder is coated on the surface of said cylindrical part, makessaid cylindrical part rotate at a speed of a predetermined intermediatedegree in said rotation range when the coating solution is coated on thesurface of said cylindrical part, and making said cylindrical partrotate at a high speed equal to or near 200 rpm after said coating layeris formed.
 25. The coating layer forming apparatus as set forth in claim9, wherein the coating solution has a viscosity of 100 CP to 20,000 CPat a coating temperature of 25° C. and a shear rate of 100 S⁻¹.
 26. Thecoating layer forming apparatus as set forth in claim 25, wherein thecoating solution is formed by an organic base resin of a binderdissolved or dispersed in water or an organic solvent and a PTFE powder,and includes 10 to 100 parts by weight of PTFE powder with respect to100 parts by weight of the organic base resin of the binder.
 27. Thecoating layer forming apparatus comprising: a rotating support devicehaving supports for detachably attaching centered between them androtatably holding two ends of a cylindrical part on which a coatinglayer is to be formed and a rotation drive for making said cylindricalpart supported by the supports rotate; a coating feeder for coating acoating solution to a surface of the cylindrical part rotating andsupported by the rotating support device; a layer forming device havinga plurality of coating formers provided along the outer circumference ofthe rotating support device, each coating former being inclined at anacute angle between the surface plane of the coating former and arotational tangential direction at the side of the coming surface ofsaid cylindrical part, having a front end positioned at a predeterminedclearance from the surface of the cylindrical part, and having aposition rotated in a reverse direction as the direction of rotation ofthe cylindrical part along the circumference of said cylindrical part,and a washing tank provided beneath said layer former and containing awashing solution for washing a coating deposited on a coating formerpositioned under it among the plurality of coating formers.
 28. Thecoating layer forming apparatus as set forth in claim 27, wherein theinclined angle of each coating former is in a range of 30 to 80 degrees.29. The coating layer forming apparatus as set forth in claim 28,wherein the rotating layer forming device successively intermittentlyrotates for each first forming step where the plurality of coatingformers form said coating solution into the coating layer.
 30. Thecoating layer forming apparatus as set forth in claim 27, wherein: arotational drive of said rotating support device makes said cylindricalpart rotate in a range of 50 to 200 rpm and the speed is increasedbefore making the front end of said coating former separate from thecoating layer of said cylindrical part.
 31. The coating layer formingapparatus as set forth in claim 27, wherein said coating former includesa layer former and a front end of said layer former facing the rotatingsurface of the cylindrical part and said front end is inclined withrespect to the surface of said cylindrical part.
 32. The coating layerforming apparatus as set forth in claim 27, wherein said coating formeris provided with a layer former and a front end of said layer formerfacing a rotating surface of said cylindrical part, a surface of saidfront end with respect to the direction of rotation of said cylindricalpart is flat, the front end has a predetermined thickness, and the rearside of the flat surface of the front end is formed cut away in an arcshape.
 33. The coating layer forming apparatus as set forth in claim 27,wherein said layer forming device has a means for adjusting a distancebetween a front end of said coating former and a surface of saidcylindrical part.
 34. The coating layer forming apparatus as set forthin claim 27, wherein said layer former: separates the front end of saidcoating former from the surface of the cylindrical part when the coatingsolution from the coating feeder is coated on the surface of thecylindrical part, makes the front end of said coating former extend to adistance defining a coating layer from the surface of said cylindricalpart when a coating is coated on the surface of the cylindrical part,and makes the front end of said coating former separate from the surfaceof said cylindrical part after the coating layer is formed.
 35. Thecoating layer forming apparatus as set forth in claim 34, wherein saidrotation drive of said rotary support device makes said cylindrical partrotate in a range of 50 to 200 rpm and said rotation drive makes saidcylindrical part rotate at a low speed equal to or near 5 rpm when acoating solution from said coating feeder is coated on the surface ofsaid cylindrical part, makes said cylindrical part rotate at a speed ofa predetermined intermediate degree in said rotation range when thecoating solution is coated on the surface of said cylindrical part, andmakes said cylindrical part rotate at a high speed equal to or near 50rpm after said coating layer is formed.
 36. The coating layer formingapparatus as set forth in claim 27, wherein the coating solution has aviscosity of 100 CP to 20,000 CP at a coating temperature of 25° C. anda shear rate of 100 S⁻¹.
 37. The coating layer forming apparatus as setforth in claim 36, wherein the coating solution is formed by an organicbase resin of a binder dissolved or dispersed in water or an organicsolvent and a PTFE powder, and includes 10 to 100 parts by weight ofPTFE powder with respect to 100 parts by weight of the organic baseresin of the binder.
 38. A method of forming a coating layer on acylindrical member, said method comprising: a first step of making acylindrical member rotate at least one rotation at a first speed, andevenly coating only a coating solution on a surface of the cylindricalmember using a coating former from a position spaced apart by apredetermined gap clearance defining a coating formation thickness withrespect to the surface of the cylindrical member to form a layer of thecoating solution on the surface of the cylindrical member; and a secondstep of making the cylindrical member rotate at a second speed higherthan the first speed, and moving the coating former apart from thesurface of the layer coated on the surface of the cylindrical member,after having rotated the cylindrical member at least one rotation at thefirst speed.
 39. The method of forming a coating layer as set forth inclaim 38, wherein in the first step, a direction of front end tip of thecoating former is inclined at an acute angle between 20 and 80 degreesto a rotational tangential direction of the cylindrical member.
 40. Amethod of forming a coating layer on a cylindrical member, said methodcomprising: approaching a tip of a coating former to a surface of acylindrical member at a predetermined gap clearance defining a coatingformation thickness; making a cylindrical member rotate at least onerotation at a first speed, and evenly coating only a coating solution ona surface of the cylindrical member by using the coating former from aposition spaced apart by the predetermined gap clearance defining acoating formation thickness with respect to the surface of thecylindrical member to form a layer of the coating solution on thesurface of the cylindrical member; and making the cylindrical memberrotate at a second speed higher than the first speed, and moving thecoating former apart from the surface of the layer coated on the surfaceof the cylindrical member, after having rotated the cylindrical memberat least one rotation at the first speed.
 41. The method of forming acoating layer as set forth in claim 40, further comprising inclining adirection of the tip of the coating former at an acute angle between 20and 80 degrees to a rotational tangential direction of the cylindricalmember.
 42. A coating layer forming apparatus comprising: a rotatingdevice for rotating a cylindrical member on which a coating layer is tobe formed at a first rotation speed for at least one rotation androtating the cylindrical member at a second rotation speed higher thanthe first rotation speed; and a layer forming device having a coatingformer, the layer forming device positioning a tip of the coating formerat a surface of the cylindrical member spaced apart by a predeterminedgap clearance defining a coating formation thickness while thecylindrical member is rotated at least one rotation at the firstrotation speed by the rotating device, and the layer forming devicemoving the tip of the coating former apart from the surface of the layerof the coating solution formed on the surface of the cylindrical memberwhile the cylindrical member is rotated at the second speed after havingrotated the cylindrical member at the first speed.
 43. The coating layerforming apparatus as set forth in claim 42, wherein a direction of thetip of the coating former is inclined at an acute angle between 20 and80 degrees to a rotational tangential direction of the cylindricalmember.